What is tromboning?

In this expert reply, Patrick Ferriter explains what tromboning means in VoIP.

What is meant by "tromboning" in VoIP?

Basically, tromboning is where RTP media traffic originates at a certain point, and follows a path out into the network and back to a destination close to where the RTP traffic originated. This is similar to the "shape" of a trombone.

IP phone 1--------|-------|---RTP Media---------------------->
                        |Switch |
) (server)
IP phone 2<-------|-------|---RTP Media-----------------------

Consider a standard SIP call as an example. Normally the SIP signaling will go to a SIP server that will set up the call between two endpoints. The endpoints typically learn each other's IP addresses and send RTP media directly to each other along the shortest path through the network (e.g. through the switch in this example). Some SIP servers may be configured to force the RTP media to go through the server itself instead of flowing over the shortest path between the endpoints. This is called tromboning.

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